Petroleum exploration and production emphasizes optimizing production of hydrocarbons from subsurface hydrocarbon reservoirs. This can include drilling multiple wells (e.g., a field of wells) into a reservoir to extract hydrocarbons (e.g., oil) trapped in the reservoir. In some instances, enhanced oil recovery (EOR) techniques are employed to assist in extracting hydrocarbons from oil and gas reservoirs. Common EOR techniques include water injection (also referred to as “water-flooding”), thermal injection, gas injection, chemical injection and the like. In the case of water injection, water is typically injected into a reservoir via one or more injection wells, to promote the flow of the hydrocarbons in the reservoir to one or more productions wells in the field.
The techniques for optimizing reservoir production often rely on accurate assessments of the reservoir, including monitoring the locations of hydrocarbons and injected fluids as they move through the reservoir. For example, it is desirable to track the progression of a slug of injected water as it moves through a reservoir to determine if and when the slug will reach a production well, and to track the location of bypassed pockets of oil still trapped in the reservoir to identify locations for additional production to extract the bypassed oil. In some instances, tracking and estimation of a waterfront (a leading edge of a pocket of injected water, also referred to as a flood-front) in a reservoir is accomplished via monitoring initial water production at production wells (referred to as “water break-through”) and a ratio of water produced versus the volume of total liquids produced at production wells (referred to as “water cut”). Unfortunately, these techniques can be complicated by the irregular structures of reservoirs. For example, in the case of tracking injected water, vertical and horizontal variations in permeability, as well as fracture corridors scattered irregularly along the length of a reservoir, can make it difficult to accurately determine where the injected water is located in the reservoir and to predict how it will move through the reservoir. This can be further exacerbated by water injections at different wellsites over extended periods of time that make it difficult to track the origin and movement of the water. For example, the Ghawar field, a super-giant conventional oil field in Saudi Arabia that is in secondary recovery using peripheral seawater injection, has a primary reservoir which includes a thick layer of carbonate sealed by anhydrite that is overlain by a second formation, which also includes a thick layer of carbonate sealed by anhydrite. Production and reservoir management for the Ghawar field is complicated by vertical (stratification) and horizontal (super-k areas) variations in permeability as well as fracture corridors scattered irregularly along the length of the field. As a result, it can be difficult to determine where injected water is located in the Ghawar field and to predict how it will move through the reservoir.